1. Technical Field
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of solving a problem such as light leakage after storing under a high-moisture environment that is actualized in a liquid crystal display device using a thin glass substrate.
2. Background Art
A liquid crystal display device is a space-saving image display device with low electric power consumption, and its use is being expanded year by year. In the related art, the liquid crystal display device has a large disadvantage that the display image has large dependency on a viewing angle, but a wide-viewing angle liquid crystal mode such as a VA mode and an IPS mode has been commercialized, and as a result, the demand for the liquid crystal display device has been rapidly expanded even in a market in which a high-quality image is required, such as in the television.
The basic configuration of the liquid crystal display device is to dispose polarizing plates on both sides of a liquid crystal cell. The polarizing plate serves to transmit only light of a polarized plane in a predetermined direction, and the performance of the liquid crystal display device greatly depends on the performance of the polarizing plate. The VA mode or the IPS mode is used as a normal black (displayed by black when voltage between electrodes in the liquid crystal cell is 0), and in this case, optical absorption axes of the polarizing plates at both sides of the liquid crystal cell are orthogonal to each other. Non-polarized light emitted from a light source transmits only polarization in a predetermined direction in the polarizing plate at the light source side, transmits the polarizing plate while the polarization state is not changed when passing through the liquid crystal cell, and is absorbed by a polarizing plate at a viewer side of which the optical absorption axis is orthogonal to the polarizing plate at the light source side. Therefore, the black display may be implemented.
The polarizing plate of the liquid crystal display device generally has a structure in which a polarizer is constituted of a polyvinyl alcohol film and the like, on which iodine or a dye is adsorbed and oriented and transparent protective films are attached on inner and outer sides of the polarizer. A cellulose acylate-based polarizing plate protective film typically of cellulose acetate has high transparency and may readily secure adhesiveness to polyvinyl alcohol used in a polarizer, and thus has been widely used as a polarizing plate protective film.
Meanwhile, recently, the usage of acryl resin has been continuously increased as the polarizing plate protective film. The background thereof is to ensure adhesion with polyvinyl alcohol by improving an adhesive technology.
In recent years, with extension of a purpose of the liquid crystal display, a large size and a high-definition texture have been required with respect to the liquid crystal display. In order to decrease a weight of a large-sized liquid crystal display, the thicknesses of various members decrease and the thickness of a glass substrate among the various members has been decreased to 0.5 mm or less from 0.7 mm in the related art. Further, in recent years, it is examined that the thickness is 0.3 mm, and the like. Further, a part corresponding to a frame such as a bezel is formed on the periphery of a screen and the width of the part decreases in order to achieve the high-definition texture.
In Japanese Patent Application Laid-Open No. 2002-6133 and Japanese Patent Application Laid-Open No. 2003-84136, color unevenness or discoloring when a polarizing plate is located under a high-temperature environment is examined and it is disclosed that the color unevenness can be enhanced by decreasing contractile force of a polarizer constituting the polarizing plate.
However, in Japanese Patent Application Laid-Open No. 2002-6133 and Japanese Patent Application Laid-Open No. 2003-84136, an enhancement of the color unevenness of the polarizing plate positioned under the high-temperature environment within a short time is proposed, while it is not noted a problem in occurrence of warp unevenness (light leakage of four corners of the panel) based on bending of a panel caused after a liquid crystal display using a liquid crystal cell, in which a glass thickness is 0.5 mm or less is positioned under a high-humidity environment for a long time.
An object solved by the present invention is to provide a liquid crystal display that can resolve a problem in warp unevenness based on bending of a panel which occurs during turn-on after storage under a high-humidity environment, which is actualized as a liquid crystal display in which the thickness of a glass substrate constituting a liquid crystal cell is smaller (for example, large size (for example, 32 inches or more) in which the thickness of the glass substrate is 0.5 mm or less).
The panel of the liquid crystal display includes the liquid crystal cell and two polarizing plates on both sides of the liquid crystal cell. When the liquid crystal display is positioned under the high-humidity environment (for example, 48 hours at 60° C. and a relative humidity of 90% and 72 hours at 50° C. and a relative humidity of 80%), any one polarizing plate of front and rear polarizing plates is also hydrated and swelled. Thereafter, when the liquid crystal display is left alone and dried, the hydrated and swelled polarizing plate is dried and contracted. Herein, from the reason that the rear polarizing plate is positioned under an environment having higher airtightness than the front polarizing plate, the front polarizing plate is more rapidly dried, and as a result, larger contractile force is generated, while the rear polarizing plate is slowly dried and small contractile force is generated. The present inventors have discovered that the panel is bent due to a difference between the contractile force of the front polarizing plate and the rear polarizing plate, and as a result, four corners of the panel contacts the bezel, thereby causing the warp unevenness (light leakage at four corners of the panel).
Therefore, the present inventors have discovered that as a result of closely examining suppression of the occurrence of the warp unevenness by decreasing the difference between the contractile force of the front polarizing plate and the contractile force of the rear polarizing plate, considering that a change in moisture content of the front polarizing plate is larger than a change in moisture content of the rear polarizing plate which is slowly dried when the liquid crystal display positioned under the high-humidity environment is dried, a moisture content just after a high-temperature high-humidity environment time elapses and just after a time elapses under a low-humidity after the high-temperature high-humidity environment time elapses is set within a predetermined range (dehydration suppression) to suppress the bending of the panel, thereby suppressing the occurrence of the warp unevenness of the front polarizing plate.
The present invention has been completed based on these findings.